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How to judge the welding quality of components

149 Published by FASTPCBA 5月 16,2019

How to judge the welding quality of components

First, welding quality requirements

When checking the welding quality of common electronic components, the electrical properties, mechanical strength and welding quality are mainly checked. Good welding quality must meet the following requirements:

(1) Good electrical performance.

High-quality solder joints should be a solid alloy layer between the solder and the workpiece metal interface to ensure good electrical conductivity.

(2) It has a certain mechanical strength.

The function of the solder joint is to connect two or more components. To make the electrical contact good, the solder joint must have a certain mechanical strength.

(3) The solder on the solder joint should be in an appropriate amount.

Too little solder on the solder joints not only reduces the mechanical strength, but also causes early solder joint failure due to the gradual deepening of the surface oxide layer. Too much solder on the solder joints not only increases the cost, but also causes the solder joints to be bridged (short-circuited), and it also cover the soldering defects. Therefore, the solder on the solder joints should be appropriate.

(4) The surface of the solder joint should be bright and uniform.

Good solder joint surface should be bright and uniform in color, free from cracks, pinholes and residue.

(5) There should be no burrs or gaps in the solder joints.

There are burrs on the surface of the solder joints, and the voids are not only unsightly, but also bring harm to the electronic products. Especially in the high-voltage shop, the tip discharge will  damage the electronic equipment .

(6) The surface of the solder joint must be clean.

The dirt on the surface of the solder joints, especially the harmful residual substances of the solder, if not removed in time, the acidic substances will corrode the leads, contacts joints and printed circuits of the components, and the moisture absorption will cause leakage or even short-circuit combustion, thus causing safety hazards.

welding

welding

Second, the typical bad solder joints appearance and its causes

(1) The peeling of the pad.

The main reason is that the pad is subjected to high temperature and is peeled off from the printed circuit board, and the defective solder joint is liable to cause a failure of the component to be broken.

(2) The solder distribution is asymmetrical.

Mainly due to the flux, solder quality is not enough, or caused by insufficient heating. The strength of the defective solder joint is insufficient, and the failure of the component is easily caused by the external force.

(3) The solder joint is whitish, uneven, and dull

Mainly due to the temperature of the soldering iron is too high, or caused by the heating time is too long. The strength of the defective solder joint is insufficient, and the failure of the component is easily caused by the external force.

(4) Tip

Mainly because the direction of evacuation of the soldering iron is wrong, or the temperature is too high, causing a large amount of flux to sublimate. This bad solder joint will cause an open circuit between the component and the wire.

(5) Cold welding, the surface of the solder joint is in the form of bean curd shape

Mainly because the temperature of the soldering iron is not enough, or the solder is shaken before the solidification of the solder. The poor solder joint strength is not high, the conductivity is weak, and it is easy to cause the component to open due to the external force.

(6) There are holes inside the solder joint

Mainly due to poor lead infiltration, or too large gap between the lead and the jack. The bad solder joint can be turned on temporarily, but the component is prone to open circuit failure over a long period of time.

(7) too much solder, too little

Excessive solder is mainly caused by the fact that the wire is not removed in time. The amount of solder is mainly caused by the premature removal of the welding wire. The strength of the defective solder joint is not high, and the conductivity is weak. It is easy to cause the failure of the component to be broken by the external force.

8) Virtual welding

Mainly because the surface of the weldment is not clean, or the flux is poor, or the heating is insufficient. The strength of the defective solder joint is not high, and the continuity of the component is unstable.

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